Self-powered model paraglider



Sept. 7, 1965 w. L. EFFINGER, JR., ETAL 3,204,358

SELF-POWERED MODEL PARAGLIDER 2 Sheets-Sheet 1 Filed Oct. 15, 1963 INVENTORS, wi iamfif 1T4.

'wan nz 8M6 BY A 7'7'0RNE Y Sept. 7, 1965 w. L. EFFINGER, JR.. ETAL 3,204,358

SELF-POWERED MODEL PARAGLIDER 2 Sheets-Sheet 2- Filed Oct. 15, 1965 A'ITORNE) United States Patent 3,204,368 SELF-POWERED MODEL PARAGLIDER William L. Efltinger, Jr., Branford, Henry Struck, Hamburg, and Wayne Gross, Cheshire, Conm, assignors to The A. C. Gilbert Company, New Haven, Conn, a

corporation of Maryland Filed Oct. 15, 1%3, Ser. No. 316,380 12 Claims. (CI. 4678) This invention relates to model para'gliders that can be flown optionally as a kite, a glider or a self-powered aircraft. Many aircraft companies are presently working on flying models of a triangular form of paraglider sometimes referred to as the flex wing. It is contemplated for use to land a space craft safely in its descent to the earth.

An object of the invention is to improve the performance of a toy version of such paraglider whose basic characteristics are the subject of a copending application, Serial No. 237,539, now Patent No. 3,153,877, owned by the assignee of the present application.

Many departures from old concepts of conventional aircraft construction must be made empiraclly to attain dependable performance of an operative paraglider and in a like manner many departures must be made empirically from the constructions of such operative aircraft to produce a model or toy paraglider that will perform successfully and yet possess the simplicity and low cost of production necessary for a toy.

Among advantages to which the present improvements are directed are the following:

To enable the craft to be flown as a tow line glider similar .to the method used for kiting.

By manipulating the tow line when the craft is in flight to detach the tow line and free the craft for untethered flight as a kite or as a self powered aircraft.

To make use of power propulsion whether the craft is tethered or released for free flight.

To supply the flexible wing sheet with reinforced uplift support relative to the spars by means that causes the sheet to assume its upwardly arched air borne shape before takeoff for flight and prevents entanglement of the sheet with a power driven propeller.

To provide means to shift and adjust the position of the center of gravity of the craft in correspondence with wind conditions at the time of flight.

To provide landing gear that insures the propeller from damage in making a landing.

To make all parts projecting widely from the main or keel spar adjustable or easily detachable from such spar in order to compact the craft for cartage or storage.

In general to provide the operator of the craft with means to experiment with various adjustments of structure and with various methods of manipulating a tow line when the craft is tethered in flight in working toward desired flight performance. Thus a youngster gaining experience and skill in playing with the toy can identify himself with the actual and exciting advances in space craft construction being widely publicized in connection with well known projects of the Space Administration known as Gemini and Apollo.

These and other objects to the invention will be evident from the following description of successful embodiments thereof having reference to the appended drawings.

In the drawings all sectioned structures appear as viewed in the direction of the arrows.

FIG. 1 is a side elevation of an aircraft incorporating the present improvements shown resting on the ground.

FIG. 2 is a bottom plan view of the aircraft with one spar and the wing sheet partially broken away.

FIG. 3 is a fragmentary view taken in section on the plane 33 in FIG. 2.

3,204,368 Patented Sept. 7, 1965 "ice FIG. 4 is an enlarged fragmentary view taken in section on the plane 44 in FIG. 1.

FIG. 5 is a still further enlarged view taken in section on the plane 55 in FIG. 2.

FIG. 6 is a similarily enlarged view in side elevation showing details of a hinge construction at the nose of the keel spar of the craft.

FIG. 7 is a fragmentary top plan view of the keel spar at the point of connection thereto of a wing spreader wire.

FIG. 8 is an enlarged elevation of the load structure or pod carrying an engine driven propeller as in FIG. 1 and fixedly depending from the keel spar.

FIG. 9 is an enlarged view taken in section on the planes 9999 in FIG. 8.

FIG. 10 is a similarly enlarged fragmentary view taken in section of the plane 1ll10 in FIG. 8 showing the storage space for liquid fuel supplied to the engine.

FIG. 11 is a perspective view of a part of the engine supporting bracket detached from the pod and incorporating a hollow that forms part of the fuel chamber.

FIG. 12 is an enlarged fragmentary view taken in secon the plane 1212 in FIG. 8 showing the mounting for the engine block on the bracket of FIG. 11.

FIG. 13 is a greatly enlarged fragmentary view taken in section on the plane 13-13 in FIG. 8.

FIG. 14 is a view in section on a similar scale taken on the plane 1414 in FIG. 8.

FIG. 15 is a view taken in section on the plane 15-15 in FIG. 8.

FIG. 16 shows on a much reduced scale the developed shape and proportions of the wing sheet before its assem- 'bly with the spars of the craft.

The overall nature of the automotive aircraft shown in the drawings is akin to that of the aircraft shown in a copending application, Serial No. 237,539, owned by the assignee of the present application. It comprises a continuous wing sheet 12 of very thin, light weight, yet tough flexible material such as vinyl light taffeta which spans two V-shaped areas separating a central fore-and-aft extending keel spar 13 and two lateral or tip spars 14 and 15 made of molded polypropylene.

The angles formed laterally by the tip spars with respect to the keel spar 13 are equal and are determined and maintained by a wing spreader 16 hereinafter more particularly described. The tip spars 14 and 15 are pivotally engaged with the keel spar 13 at the nose of the aircraft as best shown in FIG. 6. The hinge pins 22 which form the pivotal connection of the spars 14 and 15 to keel spar 13 are inclined so as to produce an upward slant of the tip spars relative to the keel spar as they extend rearward from the nose of the craft. Maintenance of this inclination of the tip spars is aided by the slanting disposition of hinge lugs 23 which hold the hinge pins 22 and project from each side of the keel spar.

The ends 18 of the stiff spreader wire 16 that engage the tip spars are bent at an angle to tuck snuggly and removably into anchorage holes 24 extending in the direction of the tip spars 14 and 15 through a bulge 26 therein. At a. midpoint of its length a loop 19 in spreader wire 16 enables the wire to swivel and be retained on a stud 17 that projects downward from keel spar 13 so that when spreader wire ends 18 are retracted from anchorage holes 24 the spreader can be turned from its full line position in FIGS. 1, 2 and 3 to a collapsed position indicated by broken lines in FIG. 2 substantially parallelling the keel spar 13. Now the tip spars can be swung inward toward the keel spar about pivots 22 also to be approximately parallel with the keel spar in their broken line positions in FIG. 2. This com-pacts the overall dimensions of the craft to save space in storage or cartage. When thus compacted the spars can be wrapped in the now loose wing sheet 12 like the fabric of a closed umbrella. FIGS.

, 3 1, 2 and 3 show that each of the half lengths of spreader wire 16 are bowed upward so as to hold the wing sheet 12 arched above the spars in the spaces separating the latter.

This orients the shape of the wing sheet to side by side inverted channels in approximation of its flying condition and thus facilitates takeoff for flight by preventing sagging of the wing sheet between the spars.

The present improvements include a construction of the stabilizer 27 differing from that in the aforesaid copending application in that the airfoil surface of the stabilizer is provided with integral or fixedly attached limber supporting legs provided at their bottom ends with a base bar 28 to which both legs 25 are fixedly attached. Bar 28 has lateral notches 29 and 30 near the bottoms of legs 25 respectively. The bottom surface-of the bar rests on the flat top surface of the front end portion of keel spar 13. The bar 28 and its upstanding legs 25 and stabilizer airfoil 27 can tilt as a unit from normal position shown in full lines in FIG. 4 to deflected positions indicated by broken lines in FIG. 4. Such tilting ofthe stabilizer is yieldingly permitted by elastic bands 31 which are looped about the notched base bar together with the keel spar. This normally stations the stabilizer yieldably in it's nontilted, squarely upright position shown in full lines in FIGURE 4. The ability of the stabilizer to deflect to its broken line positions absorbs shocks of impact when the stabilizer accidentially encounters any obstruction during flight or during the landing of the craft, or from careless handling. Studs 32 anchor one elastic band.

According to the present improvements the load structure or pod 35 is a mainly L-shaped fin integral or rigid with keel spar 13 of the craft and depending therefrom and having a foot portion 36 elongated in a direction parallel with the keel spar 13 in the direction of flight. The foot portion 36 is spaced below. the keel spar as shown in FIGS. 1 and 8. Pod 35 is equipped with a power driver propeller and with landing gear and with other equipment next to be described and which cooperate in the successful performance of the model aircraft.

The landing gear 39 comprises laterally diverging bent wire legs secured fixedly attheir upper ends to the pod 35 by a clamp screw 40 that extends through the thickness of the pod and through the looped upper ends of the landing gear wires 39, all being clamped fixedly to the pod by a nut 38 on screw 40. The designed angular position of landing gear 39 relative to the craft is dependably main-v tained by lodging wires 39 fixedly but removably in notches 41 formed by bosses 42 on opposite faces of the pod as best shown in FIG. 13. The bottom end portions of landing gear wires 39 are suitably curved to sled freely along, instead of digging into, the ground upon landing and takeoff of the craft.

To keep the propeller 45 dependably elevated above the surface on which the aircraft lands or rests before take-off the extreme rear end of keel spar 13 is provided with a rigid downward extending tail fin 61 that serves this purpose as will be clear from FIG. 1 where a straight line 62 representing ground level is seen to give clearance to the propeller 45.

Other equipment carried by the pod 35 includes an air propeller 45 powered by a miniature gasoline engine designated 46 as a Whole. The body of the engine includes a crank case 47 having mounting flanges 48 on its sides. These flanges rest on support arms 49 and 50, the former of which is a rearward projection of the pod 35 and the latter of which is a corresponding rearward projection of a bracket member 51 that is removably fastened to the pod by tie-bolts 52, 53. This bracket member is shown detached from the pod in FIG. 11. See also FIGS. 9

vand 12. Engine body flanges 48 have notches 44 to receive engine securing bolts 43 which also clamp a connecting plate 54 to the engine supporting arms 49 and and thereby add firmness and strength thereto.

A thickened portion 57 of the pod 35 together with a mating portion of bracket member 51 are each hollowed out to form when joined a barrel-shaped chamber 58 adapted to be supplied with liquid engine fuel through filler inlet 59. Fuel for engine consumption is withdrawn from chamber 58 through the tubing 60, then mixed with air and fed to the engine as in usual practice. Vacuum relief is supplied to chamber 58 through filler inlet 59. The matching edges of the two half sections of the chamber barrel 58 are joined with tongue and groove construction as shown in FIG. 10 to which may be applied any compressible substance that will insure a liquid tight seal of the joint.

.For use of the toy as a tethered, rather than a free flying, aircraft the forward extending stifl probe wire 64 is mounted on and projects forward from the front end of the foot portion 36 of pod 35 and can be adjusted and maintained in a choice of two or more angular dispositions in a vertical plane shown respectively by full lines and broken lines in FIG. 8. The front extremity of probe wire 64 is bent to a hook-shape so that a central line 65 can easily be attached or detached which line runs to the hands of an operator of the craft stationed on the ground. An inboard, looped end of probe wire 64 is secured against one side of Pad 35 by a removable holding screw 66 and the shank of the probe wire can be lodged selectively under any one of plural :springy retaining lips 67 as in FIG. 14.

The flying performance of a paraglider constructed as hereinbefore described is sensitive to. and can be altered by adjustably shifting its center of gravity forward or rearward between the nose of the craft and the tail fin 61. For this purpose the central rib 68 that upstands longitudinally of keel spar 13 is equipped with inverted U-shaped weights 72 appearing in FIGS. 8 and 15 which are slidable along rib 68 with a sufliciently frictional cling to remain in whatever positions they are set.

Finally if aid in the, upward support of tip spars 14, 15 is desired stitf bracing wires 69 may have their bottom looped ends secured to pod 35 by the same screw 40 that retains the inboard ends of the landing gear wires 39. The upper ends 70 of bracing wires 69 are bent to an angle to be removably tucked into additional anchorage holes 71 in the bulges 26 of the tip spars 14, 15. When withdrawn from such anchorage holes the bracing wires 69 will free the spars to be folded to collapsed positions as has been hereinbefore described. It should be clearly understood that the bracing wires 69 exercise no function of carrying or suspending the pod 35 and its carried equipment because the pod is completely supported by its rigid fixation to keel spar 13. Thus bracing wires 69 can only function to aid in the uplift of tip spars 14, 15 relatively to keel spar 13. In FIG. 16 the wing sheet 12 in its developed shape is seen to be provided with suitable reinforced slits 73 like button holes to accommodate parts that project downward from the spars inasmuch as the wing sheet directly underlies the spars.

The improved paraglider as herein described may be operated in the following ways.

On receiving the toy packaged in a slender long box with spars collapsed and wrapped in the flexible wing sheet and with all projecting wires and the stabilizer detached, the user'will unwrap and spread the spars and complete the assembly of the parts according to package contained instructions. An X mark on the keel spar 13 above the rear end of the pod 35 indicates a point of trial balance for the craft. The keel spar can be grasped just in front of the mark and the weights 72 moved to such position that the craft balances with the, marked point as a fulcrum. The weights can then be secured in position by rubber bands if needed. Upon trial flight if the craft tends to stall, i.e. noses upward too much, the weights should be moved forward. If the craft tends to nose dive the weights should be moved backward. It is best to have the rearends of tip spars 14 and 15 about 3% inches higher than the rear end of the keel spar.

To fly the craft as a kite the tow line 65 will be looped onto the crook of the probe 64 with the latter adjusted to its lower or broken line position in FIG. 8. The craft may then be placed on the ground in a position nosing into, say, a 15 to 20 miles per hour wind. The operator while walking away from the craft in the direction of flight will then pay out enough length of tow line to reach, say 150 to 175 feet. A quick pull forward on the line will now start the craft climbing into the wind. The line can be let out gradually depending on the wind. More pull on the line will make the craft climb. The craft can attain a height of three or four hundred feet and will remain aloft indefinitely if the wind is steady. If the wind should die down the craft will glide to a smooth three-point landing assured by the nose elevating effect of the stabilizer 27. No ordinary kite can thus perform.

Another performance possible to this craft is that of a tow-line glider for which a light wind velocity of 5 to 15 miles per hour is advantageous. The craft will be sent aloft as in the above described kiting and then towed forward by running in the direction of flight with the tow line in hand. If the line is then given a sharp pull forward and quickly released it will slip off from the crook in the probe and the craft will be on its own, or in free flight. It can be adjusted to glide in a circle in turns of about 150 feet diameter.

Both of the foregoing modes of kiting and gliding operation make no use of the crafts engine powered propeller. When the engine is to be used there are again two modes of operation, one being tethered operation and the other free flight. In engine powered operation while tethered the probe 64 is set in upper position shown in full lines in FIGS. I and 8. After attaching tow line 65 to the probe 64 the operator holding the line will advance about 50 feet forward from the craft, now resting on the ground. A helper can start the engine and hold the craft from responding to the propeller thrust. This can best be done by grasping the tail fin 61 with one hand and the rear end of one tip spar 14 or 15 with the other hand. When the craft is released by the helper the thrust of the propeller will advance it until airborne. The craft will then fly automatically in its circular path without the necessity of running with the tow line and will be more immune to wind condition than when free gliding. The supply of engine fuel can be so gauged that the engine will automatically run out of fuel, thus leaving the craft aloft without power to be kited by line control as hereinbefore described.

For powered free flight without assistance by a helper the engine is started by the operator and the craft held by grasping the tail fin 61 with one hand and grasping the ground rail of the skid wire of the landing gear 39 with the other hand. The craft can thus be held at shoulder height with the engine running and with the stabilizer 27 pointing slightly skyward and into the wind so that the wind fills out the cover sheet 12. When the craft is released the engine power will drive the craft in free flight, after which it is on its own, and will move in a circular path climbing steadily into the sky. Free flying in this manner is more satisfactory on calm days. The flight will last until fuel gives out, normally about three minutes including the time consumed in a gliding return to earth. In this length of time about a half mile Will have been traveled. If fuel supply is not limited the craft may fly out of sight and become lost in some unknown place of landing.

Within the intended coverage of the appended claims many changes can be made in the particular construction and arrangement of parts herein disclosed without departing from principles believed to be novel with this invention, wherefore it is intended that an interpretation be given to the terminology of the claims that will in- 6 clude obvious departure from the exact parts and arrangement which are herein presented merely as one example of a Successful embodiment of the improvements.

What is claimed is:

1. In a model paraglider having a fore-and-aft extending keel spar and lateral spars converging in the direction of flight toward said keel spar at the nose of the paraglider and connected to said keel spar by a flexible wing sheet, the combination with said spars and Wing sheet of, a deflectable stabilizer comprising an airfoil above said keel spar at said nose of the paraglider including at least one support leg upstanding from said keel spar below and rigid with said air foil and a foot rigid with the bottom end of said leg yieldably fastened to said keel spar in a manner to permit said rigidly related airfoil, support leg and foot base to tip as a unit relatively to said spar.

2. In a model paraglider as defined in claim 1, in which the said foot base of the said leg is joined to the said keel spar by yieldable elastic stays in a manner permitting the said stabilizer temporarily to tip relatively to said keel spar in response to impact and then automatically to right said stabilizer.

3. In a model paraglider having a fore-and-aft extending keel spar and lateral spars converging in the direction of flight toward said keel spar at the nose of the paraglider and connected to said keel spar by a flexible wing sheet, a spar spreader extending crosswise the said direction of flight from one to the other of the said lateral spars crosswise the said keel spar, said spreader being detachably engaged with said lateral spars and pivotally engaged with said keel spar in a manner to be swung into substantial alignment with said direction of flight for compacting the paraglider for carting or storage.

4. In a model paraglider, the combination defined in claim 3, in which the said spreader is bowed upward separately between each of said lateral spars and the said keel spar to a higher level than said keel spar.

5. In a model paraglider, the combination defined in claim 3, in which the said spreader is bowed upward between the said spars to a higher level than the said keel spar.

6. In a model paraglider having a fore-and-aft extending keel spar and lateral spars converging in the direction of flight toward said keel spar at the. nose of the paraglider and connected to said keel spar by a flexible wing sheet, the combination with said spars and wing sheet of, a load structure depending fixedly from said keel spar intermediate the fore-and-aft ends thereof having a foot portion extending in said direction of flight and spaced below said keel spar, a power driven propeller carried by said foot portion at the trailing end thereof with respect to said direction of flight, landing gear fixed to said foot portion of said loan structure comprising skid legs extending lower than said structure and spaced apart laterally thereof, and a tail fin carried by said keel spar near the trailing end thereof in said direction of flight depending from said keel spar a suflicient distance to maintain said power driven propeller elevated above the ground level when both said skid legs and said tail fin rest on the ground.

7. In a model paraglider having a fore-and-aft extending keel spar and lateral spars converging toward said keel spar in the direction of flight at the nose of the paraglider and connected to said keel spar by a flexible wing sheet, the combination with said spars and wing sheet of, a load structure depending fixedly from said keel spar intermediate the fore-and-aft ends thereof having a foot portion extending in said direction of flight and spaced below said keel spar, a power driven propeller carried by said foot portion at the trailing end thereof with respect to said direction of flight, landing gear fixed to said load structure forwardly of said power driven propeller in said direction of flight comprising skid legs extending downward from said structure and spaced apart laterallythereof, together with a tail fin carried by said keelspar near .the trailing end thereof in said direction of flight depending from said keel spar a sufficient distance to maintain the said power driven propeller, elevated above the ground when both the said skid legs and said tail fin rest on the ground, the relative downward extent of saidskid legs and saidtail fin being such that when both contact the ground the said keel spar is supported in an upwardly inclined wind breasting position v with respect to the ground level in said direction of flight.

8. In a model paraglider having a fore-and-aft extending keel spar and lateral spars converging in the direction of flight toward said keel spar at the nose of the paraglider and connected to said keel spar by a flexible wing sheet, the combination with said spars and wing sheet of, a keel plate of L-shaped outline joining said keel spar edgewise in rigid relation thereto and depending edgewise downward therefrom intermediate the fore-andaft ends of said keel spar and comprising toe and heel portions of said plate aligned in a common plane with said direction of flight spaced below said keel spar, a power driven propeller carried on said heel portion of said keel plate, and laterally spaced apart landing skids mounted on the toe portion of said keel plate projecting downward therefrom and straddling said common plane.

9. In a model paraglider having a fore-and-aft extending keel spar and lateral spars converging in the direction of flight toward said keel spar at the nose of the paraglider and connected to said keel spar by a flexible wing sheet as defined in claim 8, a weight mounted on the said keel spar in a manner to be shifted to selective position therealong fortvarying the Icenter of gravity ofthe paraglider in said direction of flight.

10. In a model paragliderhaving a fore-and-aft extend:

ing keel spar and lateral spars converging in the direction of flight toward said keel spar at the nose of the paraglider and connected to said keel spar by a flexible wing sheet, the combination with said spars and wing sheet of, a unitary load body of solid material depending fixedly from said keelspar intermediate the fore-and-at't ends thereof having a foot portion extending in said direction of flight and spaced below said keel spar, a power driven propeller carried by said foot portion at the trailing end thereof with respect to said direction of flight, a liquid fuel consuming combustion engine carried by said load body connected to power said propeller, and a hollow in said load body forming a chamber adapted to contain said liquid fuel.

11. Ina model paraglider having a fore-and-aft extending keel spar and lateral spars converging in the direction of flight toward said keel spar at the noseof the paraglider and connected to said keel sparby' a flexible wing sheet, the combination with said spars and wing sheet of, a unitaryv load body depending fixedly from said keel spar intermediate the fore-and-aft ends thereof having a foot portion extending in said direction of flight and spaced below said keel spar, a power driven propeller carried by said foot portion at the trailing end thereof with respect to said direction of flight, a liquid fuel'consumingcombustion engine carried by said load body connected to power said propeller, and a hollow in said load body forming a chamber adapted to contain said liquid 'fuel, said load body being split into mating sections in planes intersecting said hollow whereby the walls of said chamber are separable andcan be produced as separable parts of said, load body.

12. In a model paraglider having a fore-and-aft extending keel-spar and lateral spars converging in the direction of flight toward said keel spar at the nose of the paraglider and connected to said keel spar by a fiexible wing sheet, the combination with said spars and wing sheet of, a keel plate of L-shaped outline joining said keel spar edgewise in rigid relation thereto and depending edgewise downward therefrom intermediate the fore-and-aft ends of said keel spar and comprising toe and heel portions of said plate aligned in a common plane with said direction of flight spaced below said keel spar, a powerdriven propeller carried on said heel portion of said keel plate, and laterally spaced apart landing skids mounted, on the toe portion of said keel plate projecting downward therefrom and straddling jsaid common plane, together with a stiff cantilever probe rod, projecting forward frornsaid toe portion of said keel plate in said direction ,offlight having means to mount the former adjustably in selective positions of slant in a vertical plane, relative to the latter, whereby the forward extremity of said probe rod can be raised or lowered with respect to said keel spar.

References Cited by the Examiner UNITED STATES PATENTS 1,010,585 12/11 Carter 4 678 1,035,017 8/12 Kaiser 46-78 1,545,553 7/25 Dillingham 244'49 1,549,073 8/25 Dwyer 46--78 2,373,236 4/45 Efiinger 2443 3,102,703 9/63 Armstrong 2443 3,153,877 10/64 Effinger et al. 244l6 X FERGUS S. MIDDLETON, Primary Examiner. I RALPH D. BLAKESLEE, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No."3',2'04,3"68' September 7, 1965 William L. Effinger, Jr., et a1."

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 13, after "foot" insert base line 54, for "loan rezid load Signed and sealed this 15th day of March 1966.

( L) Amen ERNEST w. SWIDER EDWARD -J. BRENN Attesting Officer Commissioner of Patents 

1. IN A MODEL PARAGLIDER HAVING A FORE-AND-AFT EXTENDING KEEP SPAR AND LATERAL SPARS CONVERGING IN THE DIRECTION OF FLIGHT TOWARD SAID KEEP SPAR AT THE NOSE OF THE PARAGLIDER AND CONNECTED TO SAID KEEL SPAR BY A FLEXIBLE WING SHEET, THE COMBINATION WITH SAID SPARS AND WING SHEET OF, A DEFLECTABLE STABILIZER COMPRISING AN AIRFOIL ABOVE SAID KEEL SPAR AT SAID NOSE OF THE PARAGLIDER INCLUDING AT LEAST ONE SUPPORT LEG UPSTANDING FROM SAID KEEL SPAR BELOW AND RIGID WITH SAID AIR FOIL AND A FOOT RIGID WITH THE BOTTOM END OF SAID LEG YIELDABLY FASTENED TO SAID KEEL SPAR IN A MANNER TO PERMIT SAID RIGIDLY RELATED AIRFOIL, SUPPORT LEG AND FOOT BASE TO TIP AS A UNIT RELATIVELY TO SAID SPAR. 